A control method of this kind is known, for example, from U.S. Pat. No. 5,921,313 A. The known control method only has one single oscillating compensator. In this case, the sum of the interference frequency components is identical to the sole interference frequency component determined.
The various embodiments disclosed herein also relates to a computer program, which comprises a machine code, which can be implemented directly by a control device for a continuous casting machine and the execution of which by the control device causes the control device to control the meniscus of a continuous casting mold of the continuous casting machine according to a control method of this kind.
The various embodiments disclosed herein also relates to a control device for a continuous casting machine, which is embodied in such a way that, in operation, it executes a control method of this kind.
Finally, the various embodiments disclosed herein relates to a continuous casting machine, which is controlled by a control device of this kind.
During continuous casting, the cast strand is withdrawn from the continuous casting mold while the core of the strand is still liquid. When the strand has emerged from the continuous casting mold, the strand is guided and supported over roll pairs to support the strand shell against the metallostatic pressure of the core. The support prevents inter alia bulging of the cast strand on the broad side of the strand. The spacing of the rolls, which support the strand at the same point on both sides, must correspond to the desired strand thickness.
After emerging from the continuous casting mold, the cast strand is actively and/or passively cooled. The cooling causes the strand thickness to shrink. For this reason, the rolls supporting the cast strand at the same point on both sides must have the correct spacing from each other. Until complete solidification, also known as the crater end, the cast strand has not completely solidified. Therefore, it has a liquid core. Therefore, uneven impacts on the strand as it passes through the roll pairs exert an effect on the meniscus. However, for various reasons, for example due to the risk of casting powder being drawn into the surface of the strand, meniscus level fluctuations should be avoided where possible.
Fluctuations in the shell thickness that develop in the continuous casting mold can result in the occurrence of so-called “unsteady bulging” when passing through the roll pairs. The “bulging” is caused when a point with impaired shell thickness passes through different roll pairs one after the other and the meniscus therefore undergoes cyclical changes. Since, when viewed in the direction of transport of the strand, the roll pairs generally have constant spacing from one another and the withdrawal speed at which the strand is withdrawn from the continuous casting mold is constant, “unsteady bulging” results in periodic changes in the meniscus level. Consequently, oscillations with a constant frequency form in the meniscus.
The control method known from U.S. Pat. No. 5,921,313 A has the object of overcoming meniscus fluctuations of this kind. The known control method already works very well. In particular, it enables the meniscus to be regulated precisely to a few millimeters.
From the specialist article “Suppression of Periodic Disturbances in Continuous Casting using an Internal Model Predictor” by C. Furtmueller and E. Gruenbacher, IEEE International Conference on Control Applications, Munich, Germany, Oct. 4-6, 2006, pp. 1764 to 1769, a control method is known for the meniscus of a continuous casting mold in which the inflow of liquid metal into the continuous casting mold is set by means of a closure device and the partially solidified metal strand is withdrawn from the continuous casting mold by means of a withdrawal device. A measured actual value of the meniscus is fed to a meniscus controller, which determines a target position for the closure device on the basis of the actual value and a corresponding target value. The motor currents from drives of the withdrawal device are subjected to a frequency analysis. The components of a fundamental frequency and its harmonic frequencies are used to determine a disturbance variable compensation value, which is connected to the output signal of the meniscus controller. The closure device is controlled according to the output signal of the meniscus controller corrected in this manner.